The present invention relates to rail bogies and, more particularly, to a separable rail bogie for use in conjunction with convertible rail-highway vehicle systems which employ separable rail bogies.
Convertible semi-trailer vehicles having over-the-road or highway running gear with rubber-tired wheels and a separable flanged-wheel rail bogie are known, generally. In these vehicles, the semi-trailer body is supported upon the highway running gear during over the road travel and is supported on a rail bogie during travel over railroad tracks. A retractable mounting is provided for the highway wheels so that they can be raised or lowered for selective use of the vehicle in the railway mode or highway mode of travel, respectively. Alternately, the highway running gear can be detachably mounted so that it may be removed in its entirety from the semi-trailer body when attachment to a rail bogie for railway travel is desired. The highway running gear can be of the single-axle or the tandem-axle type. In each case, each axle carries sets of tires of conventional size which allow maximum loads to be carried as legally permissible. The rail bogie is detached from the semi-trailer body for operation of the vehicle in the over-the-road or highway mode of travel.
Rail bogies are known, generally, as are separable rail bogies for convertible rail-highway vehicles and are shown for example in U.S. Pat. Nos.: 4,538,524, 4,332,201, 3,712,245, 3,358,615, 2,758,549, 2,036,535, 2,963,986, 4,276,968, 4,316,640, 4,387,933, 4,448,132, and 4,574,707. Heretofore, however, separable rail bogies provided for convertible rail-highway vehicles were generally based upon conventional railroad bogies as used on railway cars with a few added features so that such a rail bogie can be releasably attached to a semi-trailer vehicle. In other words, the basic idea of convertible rail-highway vehicles with separable rail bogies was to take a conventional rail bogie or truck and add a special attachment structured to enable attachment to a trailer.
One problem with so modifying a conventional railroad bogie is that standard railway bogies have steel-spring suspensions. Thus, as load changes are encountered in the semi-trailer body, the rail bogie springs will simply compress more in response to the added load. This changes the ride height of the semi-trailer vehicle, making the same closer to the railway tracks as the load in the vehicle increases. This change in ride height can be as much as three inches, which renders the clearance between the rails and the highway wheels which have been retracted for railway travel insufficient.
Another problem with the variance in ride height is when one semi-trailer vehicle in the rail mode is to be coupled to an adjacent vehicle. If the two vehicles are carrying loads of different weights, the ride height of each vehicle will be different and the coupling of the two vehicles will be difficult. The above-mentioned problems associated with steel-spring rail bogie suspensions may be minimized by providing stiffer springs so that ride height variances are minimized. However, providing stiffer springs deteriorates the quality of ride.
Another problem associated with the provision of conventional rail bogie steel-spring suspension is encountered when a semi-trailer body is to be detached from the rail bogie for operation in the highway mode. When a large load is carried in the semi-trailer body, the resulting reduced ride height in the rail mode means that the highway wheels, once lowered to their ground-engaging position, must then provide the energy to lift the vehicle body sufficiently so as to enable its disengagement from the rail bogie. Indeed, even if the semi-trailer body is empty, its own dead weight will compress the springs of a conventional rail bogie from their unloaded state, requiring the vehicle's highway wheels to raise the vehicle body for disengagement from the rail bogie. The lower the ride height of the vehicle when in the rail mode, the more work must be done by the highway wheels, which slows the process of changing from the rail mode to the highway mode of operation.
Another difficulty encountered with the railway bogies heretofore provided is that the side-frames of the rail bogie may move longitudinally relative to one another into a "parallelogram" mode. Parallelogramming is a very undesirable misalignment of the axles which may result in premature wheel wear or bogie instability. For proper operation, the bogie axles should remain perpendicular to the sideframes at all times.
Yet another difficulty encountered with the provision of conventional rail bogies is that conventional railway cars are designed so that all of their weight is carried by the center of the cross-structure or bolster of the associated rail bogie. Because of this practice, the cross-structure or bolster of conventional bogies is a massive, strong, and heavy structure, as it must at times support a load on the order of fifty tons. Because the bolster is so massive, conventional rail bogies are very heavy, making transport and repeated coupling operations in conjunction with convertible rail-highway vehicles time consuming and difficult.
Even further, because the conventional bolster structure is so large and heavy, there is very little space available on a conventional rail bogie for the installation of brake equipment. The brake equipment necessary for operation in the rail mode is typically very expensive and relatively bulky. Ideally, the brake equipment should be provided on the rail bogies rather than on the highway semi-trailer bodies of convertible rail-highway vehicles so that the equipment will not be damaged during operation over highways. Further, providing the brake equipment on an associated rail bogie enables repair of the equipment without withdrawing the entire semi-trailer body from the transport system.
In view of the foregoing, it would be desirable to provide a rail bogie for convertible rail-highway vehicle systems employing separable rail bogies that addresses the disadvantages of conventional rail bogies and which can be effectively used under actual operating conditions.